Get used to this word..... REASONABLE. I hated it, I still hate it, but tit is the best standard we have. Last summer a guy drove his car into me on purpose. We had a pretty heated exchange. I didnt like where this was headed so I got back into my car, seat belt was on, im in a convertible miata, down low, and very much defenseless. The guy threatened to beat my arse, and walked about 10 ft very fast up to my car and opened my car door. Did I have reason to believe his threat? Prosecutors and juries are asked a simple question. Under the circumstances, would a reasonable person believe this person's threat and give you reason to fear for your safety? If so, assault just took place, whether he actually touched you or not.
By the way, the guy that opened my door could have been shot and killed if I wasnt cool under pressure. My gun was six inches from his chest, and he did what I wanted, he backed up, we both drove away and he lived for another day.